Many hearing loss patients have some degree of residual hearing in the low frequencies (e.g., below 1 kHz) and a severe hearing loss in the high frequencies (e.g., above 1 kHz). These people cannot benefit from traditional hearing aid amplification because of the severity of the hearing loss in the high frequencies. Nor are they classic cochlear implant candidates, because of their mostly intact low frequency residual hearing.
For this group of people, electro-acoustic stimulation (“EAS”) systems have been developed that provide such patients with the ability to perceive both low and high frequencies. Electro-acoustic stimulation combines the functionality of a hearing aid and a cochlear implant together in the same ear by providing acoustic stimulation representative of low frequency audio content and electrical stimulation representative of high frequency content. The auditory nerve combines the acoustic and electric stimuli into one auditory signal. Results of various studies have shown that electro-acoustic stimulation may enhance speech understanding, pitch discrimination, and music appreciation.
Unfortunately, an EAS patient may have one or more regions in his or her cochlea that contain no (or very few) functioning inner hair cells (or simply “hair cells”) and/or neurons. Such regions are referred to as “dead regions” and, if located at positions within the cochlea corresponding to the relatively low frequencies typically represented by acoustic stimulation, can impair the EAS patient's ability to perceive sounds represented by the acoustic simulation.